The World Health Organization estimates that over 350 million people are at risk of developing leishmaniasis and infection prevalence is 14 million people in the world. Annually, 2 million people are infected with Leishmania species and 270,000 will die. Leishmaniasis is one of the most important parasitic diseases affecting the U.S. military today, with over 2500 U.S. military personnel diagnosed with cutaneous leishmaniasis (CL). Current non-immunization based treatments are variably effective, highly toxic, expensive, and there are no vaccines in clinical use. Significant evidence has supported the role of the immune system in controlling Leishmania infection. Thus, a vaccination remains an attractive disease prevention strategy. Two significant scientific knowledge gaps must be addressed: 1) a vaccine that can access the skin resident dendritic cells (DCs), and 2) the identification of Leishmania antigens that are biologically relevant in humans. Needle based vaccines bypass these immunopotent skin cells. The long-term objective of this proposal is to develop a nanoscale polymersome-based vaccine that delivers an antigen and adjuvant to skin dendritic cells through transfollicular immunization (TFI). We will characterize the feasibility of integrating the Toll-like receptor 7/8 agonist resiquimod (RSQ) into the polymersome membrane and encapsulating a model Leishmania antigen, Leishmania homolog of receptors for activated C kinase (LACK), into the aqueous core. We will then evaluate its functional properties in generating a TH1-type cytokine profile and functional cytotoxic CD8+ T cells in vivo. We hypothesize that co-encapsulation of LACK and RSQ into the nanovaccine can be achieved in a stepwise manner and that the resulting nanovaccine will penetrate the follicle and activate skin DCs. We also hypothesize that the topical administration of this nanovaccine will induce a LACK-specific T cell response. Finally, we hypothesize that this nanovaccine will protect against challenge with a visceral Leishmania strain in a hamster model. AIM 1 Construct a nanovaccine encapsulating the antigen LACK and TLR7/8 agonist RSQ (LACK/RSQ-NPS). AIM 2 Determine the optimal physicochemical properties of LACK/RSQ-nanovaccine to penetrate the follicular duct, activate skin DCs, and induce a LACK-specific adaptive immune response. AIM 3 Determine if the LACK/RSQ-nanovaccine induces protective immune responses in vivo. We anticipate the data generated from this proposal will result in a commercially viable topical nanovaccine that can access skin DCs via the transfollicular route. The NIAID supports basic, preclinical, and clinical research on immune-mediated diseases such as leishmaniasis and the development of effective vaccines. The aims proposed in this SBIR Phase I program are consistent with the mission statement of the NIAID.